1. Field of Art
This disclosure relates generally to orifice fittings for measuring fluid flow rates. More particularly, the disclosure relates to an orifice plate assembly for use in orifice fittings.
2. Description of Related Art
Fluid flow rate is the quantification of bulk fluid or gas movement, typically measured as volumetric and mass flow rates. The ability to measure reliably and accurately fluid flow rates serves an important function in a variety of processes and industries (e.g, chemical processing, oil and gas transport and production, etc.).
An orifice fitting is one of many devices that may be used to measure volumetric or mass flow rate of fluids flowing through a pipe or conduit. An orifice fitting typically employs a flat, thin plate having a central orifice that is smaller in diameter than the diameter of the conduit in which the plate is disposed. The orifice plate is positioned between a sealing ring and a compression ring that are held together by a fastener to form an orifice plate assembly. The orifice plate assembly is disposed within a plate carrier, which is, in turn, supported and aligned within the orifice fitting. The mass fluid flow rate through the conduit is calculated from the pressure differential across the orifice plate, the static pressure, the temperature, the density of the fluid flowing through the conduit, the diameter of the conduit, and the orifice size.
When using an orifice plate to measure fluid flow, there are many factors to be considered in obtaining accurate flow measurements. The configuration and arrangement of seals within the orifice plate assembly is an important consideration. In particular, one or more seals may be provided in the orifice plate assembly to reduce the potential for flowing fluid to leak out of the orifice plate assembly between the orifice plate and sealing ring. Fluid leakage from the orifice plate assembly may result in erroneous flow measurements.
Conventionally, the seal ring is typically positioned on the upstream side of the orifice plate, and the compression ring is positioned on the downstream side of the orifice plate when the orifice plate assembly is positioned within the orifice fitting to measure flow rates. In some conventional orifice plate seal assemblies, a seal may be provided between the seal ring and orifice plate, but no seal is provided between the orifice plate and the compression ring. In such assemblies, if the compression ring side of the orifice plate assembly is inadvertently positioned upstream when the assembly is positioned within the orifice fitting, leakage may occur, thereby detrimentally affecting flow measurements. Thus, such assemblies are considered to be uni-directional, meaning such conventional assemblies may permit accurate flow measurements when flow passes through the assembly in one, but not both, directions.
The composition of the seals is also an important consideration. In some conventional orifice plate seal assemblies, the seal includes an elastomeric material. Depending on the fluid passing through the assembly, the seal material may be incompatible with the fluid. In instances when the seal material is incompatible with the fluid, leakage may result, again detrimentally affecting flow measurements.
The mechanism securing the sealing ring and compression ring about the orifice plate is yet another important consideration. In some conventional orifice plate seal assemblies, a metal clip is used to secure the assembly. This introduces manufacturing complexity due to an additional part that must be made within tight tolerances. In the event that the metal clip is not within design tolerances, leakage may result during use. Additionally, the assembly may come apart when the plate carrier is removed from the fitting. Over time, fluid passing through the assembly may corrode the metal in the clip, resulting in failure of the clip to securely hold the assembly together. This too may lead to leakage during use and/or the assembly coming apart during removal from the fitting.
In other conventional orifice plate seal assemblies, a locking mechanism securing the sealing ring and compression ring together is machined into the compression ring and/or sealing ring. For example, a lip may be machined in the compression ring to engage a matching groove in the sealing ring. As with the metal clip, this increases manufacturing complexity. Also, leakage may occur when the lip and groove are not manufactured within design tolerances. Moreover, the plastic behavior of the compression ring and sealing ring materials may limit the number of times these rings may be assembled, disassembled, and reassembled while still providing a secure locking mechanism for the assembly.
Lastly, the configuration and arrangement of the orifice plate assembly may impact tolerancing, manufacturing complexity, and associated manufacturing costs. In general, manufacturing costs of an orifice plate assembly may be reduced by reducing the number of components required to reliably seal the orifice plate. Additional components may result in additional inventory requirements (e.g., stock on-had of each component) at the operations site, may result in increased tolerancing demands for each individual part so that the combined orifice plate assembly is reliably sealed, and may require additional manufacturing/repair steps. Each of these consequences may contribute to increased manufacturing costs and complexities.
Thus, reliable means to seal the orifice plate of an orifice fitting are desirable. Methods and devices for orifice plate seal assemblies which ease manufacturing or installation complexities, or which reduce cost, would likewise be particularly desirable.